The invention relates to a method for controlling several stepping motor modules in which each respective power unit of the step motor modules supplies at least one step motor with current impulses, with the step motor being advanced one step by each current impulse. A power unit receives impulses that are separated in time from a logic assembly, the edges of which pulses generate a current pulse in the power unit and the interval of which relative to the previous pulse is acquired from a set of ramp data. Furthermore, the invention relates to a device for carrying out the method.
Stepping motor modules are used particularly in printing and copying devices to drive transport drums, which transport the paper or forms that are to be printed through the printing or copying device. WO 98/18060 A1 describes a printing device, for example.
The stepping motors in printers or copiers are accelerated or braked according to a prescribed rate-of-rotationspeed curve. This speed/time curve for acceleration is also called a ramp. To control the running up and braking of the stepping motor, the possibility exists for a device control to supply the logic assembly with the required ramp data continuously. This type of system is described in Teodorescu, EMA 90/4, s. 106-109 (FIG. 3). A similar system is known from De 25 11 640 A. In these types of systems, when a plurality of ramp data requires a transfer in real time, the technical expense that is required for this, both on the device control side and the stepping motor module side, rises significantly. Another problem arises when the ramp data are supplied via a bus system. Since the bus system has fluctuating reaction times, it is not guaranteed that the ramp data that are output the device control are converted into the required rotation steps for the stepping motor with ever more constant delay. Rather, this delay depends on the current usage of the bus system, so that the step motor is not run up and braked precisely to the prescribed ramp. This problem has a particularly adverse effect when several stepping motor modules are supplied with ramp data by the device control unit, and the relevant stepping motor has to follow identical ramps in order to provide identical transport speeds.
The article xe2x80x9cServoantriebexe2x80x94vom einfachen Steller zum intelligente Systembausteinxe2x80x9d (Weidauer, AGT 4/96, pp. 14-18) and DE 39 28 451 A1 teach stepping motor systems in which several servo drives in a more complex system each have a separate logic. To reset the drive characteristic, new parameters can be loaded from the outside.
U.S. Pat. No. 4,568,866 teaches a method for controlling stepping motors in which ramp data are loaded into stepping motor modules in advance. A plurality of modules that are supported by microprocessors work in conjunction with one another in such a way that different stepping motors can be actuated at the same time. The ramp data are calculated centrally in computer and transferred via a bus system to the modules for actuating the stepping motors.
It is an object of the invention to propose a method and a device for controlling a stepping motor module which has high flexibility and which guarantees, under real time conditions, that the required acceleration and delay ramps are precisely followed.
According to the invention, a method is put forward for controlling at least one stepping motor of a stepping motor module, in which a power unit of the stepping motor module supplies at least one stepping motor with power, with the stepping motor advancing one step with each current impulse. The power unit receives impulses from a logic assembly, whose respective edge generates a current impulse and whose respective interval relative to the previous impulse is computed from a set of ramp data. The logic assembly reads ramp data that follow upon one another at definite time intervals in order to define the pulsewidth of the respective pulsewidth modulated pulse. In the logic unit, several sets of ramp data are made available. The sets of ramp data are computed in advance centrally in a computer and are transferred via a bus system to the logic assembly in a loading phase prior to the operation of the stepping motor. The current set of ramp data are communicated to the stepping motor module during the operation of a control unit via the bus system. The conversion of the set of ramp data that is selected in the logic assembly into impulses with a variable interval is started by a start signal.
In the invention the sets of ramp data which define the rising ramp in the acceleration of the stepping motor and the trailing ramp in the braking of the stepping motor are calculated in a computer during the loading phase; that is, outside the scope of the actual operating of the stepping motor module. The rules and parameters for this calculation are predetermined by characteristic attributes of the stepping motor, on the one hand, and by the respective characteristics that are desired in the application, on the other hand.
Calculation formulas for calculating the ramp data are prescribed on a motor-specific basis. The sets of ramp data that are obtained by the calculation are transferred to the respective logic assembly via a bus system and stored there. Because the calculation occurs outside the scope of the actual operation phase, there is sufficient time to be able to use complex and accordingly precise formulas.
With the invention, it is possible in particular to store all computed sets of ramp data decentrallyxe2x80x94that is, in the individual stepping motor modulesxe2x80x94once, in a non-volatile memory, and to use these data as needed depending on the operation. In particular, it can be provided that the currently needed data be loaded from the non-volatile memory into a volatile main memory, the access time of the volatile memory in the operation being appreciably shorter than that of the non-volatile memory. This makes it possible to control the stepping motor, a plurality of stepping motors, in real time.
During the operation of the stepping motor module, the logic assembly can be informed of the current ramp dataxe2x80x94i.e. that which is being requiredxe2x80x94by the device control unit, namely via the bus system. This set of ramp data then stipulates the speed/time curve of the stepping motor. The transfer via the bus system of a logical name or a characteristic digit for the set of ramp data that are to be selected is not time-critical and can be performed in the real-time operation, even given simple bus systems and interface systems.
According to the invention, an additional start signal is sent to the logic assembly, whereupon the conversion of the ramp data into pulsewidth modulated impulses is begun. In this way, the transmission of the logical name of the selected set of ramp data and the actual start process for modifying the rate of rotation of the stepping motor are decoupled with respect to time. For instance, in several stepping motor modules the sets of ramp data that are needed for a particular motion sequence of the stepping motors can be designated in that the required sets of ramp data are communicated in a data transfer process which is shifted in time and is thus not time-critical. The time-critical start signal, which can be transferred without a large data transmission expense and thus in a short time window, is output only at a later time, and the conversion of the ramp data is begun.
For time-critical applications, the start signal is transferred via a separate line which is separate from the bus system. This way, the reaction time of the bus system and its usage are unimportant. Rather, several stepping motor modules can receive the start signal exactly at the same time, so that identical speed/time curves can be followed by several step motors simultaneously.
According to another aspect of the invention, a device for controlling at least one stepping motor module is laid out as claimed in claim 10. This device has the beneficial effects already described for the method.
Exemplifying embodiments of the invention will now be detailed with the aid of the drawing.